Time-resolved X-ray microscopy of nanoparticle aggregates under oscillatory shear

Of all current detection techniques with nanometer resolution, only X-ray microscopy allows imaging nanoparticles in suspension. Can it also be used to investigate structural dynamics? When studying response to mechanical stimuli, the challenge lies in applying them with precision comparable to spatial resolution. In the first shear experiments performed in an X-ray microscope, we accomplished this by inserting a piezo actuator driven shear cell into the focal plane of a scanning transmission X-ray microscope (STXM). Thus shear-induced reorganization of magnetite nanoparticle aggregates could be demonstrated in suspension. As X-ray microscopy proves suitable for studying structural change, new prospects open up in physics at small length scales.Comment: submitted to J. Synchrot. Radia

Between-Person Disparities in the Progression of Late-Life Well-Being

Throughout adulthood and old age, levels of well-being appear to remain relatively stable. In this chapter, we argue that focusing on a phase of life during which this positive picture does not necessarily prevail promises to help us better understand between-person disparities in the progression of late-life well-being. In a first step, we review empirical evidence from the German Socio-Economic Panel and other large-scale longitudinal data sets to demonstrate that ubiquitous reports of a "stability-despite-loss phenomenon" of well-being do not generalize into years of life immediately preceding death. Instead, mean-level representations of the end of life are characterized by a rapid deterioration in well-being. In a second step, we highlight the vast heterogeneity in how people experience the last years and consider the role of biopsychosocial individual difference factors to account for such disparities. The select factors reviewed here include socio-demographic characteristics, cognitive fitness, pathology, and disability. In a third step, we argue that macro-contextual factors such as the social, service, and physical characteristics of the communities and societies people are living and dying in also profoundly shape the nature and progression of individual late-life well-being. Our conceptual reasoning forecasts some of the insights that can be gained by pursuing this line of research, but also underscores the challenges researchers must deal with.Late-Life Well-Being, SOEP, BHPS, HRS

Collisional strong-field QED kinetic equations from first principles

Starting from nonequilibrium quantum field theory on a closed time path, we derive kinetic equations for the strong-field regime of quantum electrodynamics (QED) using a systematic expansion in the gauge coupling $e$. The strong field regime is characterized by a large photon field of order $\mathcal{O}(1/e)$, which is relevant for the description of, e.g., intense laser fields, the initial stages of off-central heavy ion collisions, and condensed matter systems with net fermion number. The strong field enters the dynamical equations via both quantum Vlasov and collision terms, which we derive to order $\mathcal{O}(e^2)$. The kinetic equations feature generalized scattering amplitudes that have their own equation of motion in terms of the fermion spectral function. The description includes single photon emission, electron-positron pair photoproduction, vacuum (Schwinger) pair production, their inverse processes, medium effects and contributions from the field, which are not restricted to the so-called locally-constant crossed field approximation. This extends known kinetic equations commonly used in strong-field QED of intense laser fields. In particular, we derive an expression for the asymptotic fermion pair number that includes leading-order collisions and remains valid for strongly inhomogeneous fields. For the purpose of analytically highlighting limiting cases, we also consider plane-wave fields for which it is shown how to recover Furry-picture scattering amplitudes by further assuming negligible occupations. Known on-shell descriptions are recovered in the case of simply peaked ultrarelativistic fermion occupations. Collisional strong-field equations are necessary to describe the dynamics to thermal equilibrium starting from strong-field initial conditions

Increasing the bandwidth of resonant gravitational antennas: The case of Explorer

Resonant gravitational wave detectors with an observation bandwidth of tens of hertz are a reality: the antenna Explorer, operated at CERN by the ROG collaboration, has been upgraded with a new read-out. In this new configuration, it exhibits an unprecedented useful bandwidth: in over 55 Hz about its frequency of operation of 919 Hz the spectral sensitivity is better than 10^{-20} /sqrt(Hz) . We describe the detector and its sensitivity and discuss the foreseable upgrades to even larger bandwidths.Comment: 4 pages- 4 figures Acceted for publication on Physical Review Letter

Paleocene Radiolaria from DSDP Leg 36-Site 329, Maurice Ewing Bank, Malvinas Plateau: biostratigraphic response

The carbonatic succession of the Maurice Ewing Bank in the Malvinas Plateau, presents records of remarkable paleoceanographic changes in the South Atlantic Ocean, and documents the interval between its opening and the stabilization of the circumpolar current. A report of the Paleocene radiolarian fauna recovered in the Cores 33 and 32 (Section 4) of the DSDP Leg 36-Site 329 is presented herein. The samples, composed mainly by micritic limestones, were chemically treated with a solution of hydrogen peroxide (H2O2) and sodium hexametaphosphate (Na16P14O43). Afterward, they were soaked in a solution of chloridric acid (HCl). The studied microfauna shows low diversity and abundance and is composed by the genera Amphisphaera, Haliomma, Amphymenium, Spongodiscus, Lithelius, Dictyomitra, Dendrospyris, Bathropyramis and Siphocampe. The original biostratigraphic framework proposed for the DSDP Leg 36-Site 329 (based on nannofossils and foraminifers) assigns a Paleocene age to the rocks of the Cores 33 and 32 (Section 4). Radiolarian absence in the Paleocene-Oligocene interval is due to the poor preservation of the specimens. However, the co-occurrence of Amphisphaera priva (Foreman) Hollis and Dictyomitra andersoni (Campbell and Clark) Foreman allows us to sustain at least a Late Paleocene age for the Core 33. The assemblages recovered in the Cores 33 and 32 (Section 4) exhibit some similarity with Paleocene faunas reported in the New Zealand region. Forthcoming studies based on this radiolarian microfauna can provide relevant paleoceanographic data about the South Atlantic Ocean during the Late Paleocene.Simposio VI: Microfósiles del Mesozoico y Cenozoico de América del Sur y Antártida. Nuevas aplicaciones y problemáticas asociadasFacultad de Ciencias Naturales y Muse

The Electronic and Magnetic Properties of Cation Ordered Sr2Mn2.23Cr0.77As2O2

ACKNOWLEDGMENT This research is supported by the EPSRC (research grant EP/L002493/1). We also acknowledge the UK Science and Technology Facilities Council (STFC) for provision of beam time at the ILL.Peer reviewedPostprin

Magnetoelectric and structural properties of Y2CoMn O6: The role of antisite defects

We have carried out an investigation on the magnetoelectric properties of the presumed multiferroic Y2CoMnO6 with different degrees of Co/Mn atomic ordering. The magnetic ground state was studied by neutron diffraction, showing a collinear ferromagnetic (FM) ordering of Co and Mn moments with a small antiferromagnetic canting. No superstructure peaks from an E-type magnetic structure were detected in our measurements. Magnetic measurements reveal FM transitions with pinned magnetic domains. The degree of Co/Mn ordering affects the Curie temperature only a little, but has strong effects on the magnetic hysteresis loops, and the FM moment signal at high field increases with increasing such order. The loops display steps at critical fields whose number and extent depends on each specimen. The most ordered sample exhibits the greatest steps ascribed to the alignment of magnetic domains separated by antiphase boundaries. All samples are insulators exhibiting low dielectric loss and dielectric constants at low temperature. On warming, they show a step increase in the real dielectric permittivity accompanied by peaks in the dielectric loss typical of thermally activated hopping processes. At room temperature, the huge values of the dielectric constant reveal the presence of Maxwell-Wagner depletion layers. Pyroelectric measurements reveal a high polarization at low temperature for these compounds that increases with increasing the Co/Mn ordering. There is no correlation between the magnetic transition and the onset of pyroelectric current. No significant changes are observed in the pyroelectric effect measured under an external magnetic field, so magnetoelectric coupling is negligible. This paper identifies the pyroelectric current as thermally stimulated depolarization current ascribed to the reorientation of defect dipoles with activation energy of about 0.05 eV. Therefore, no ferroelectric transition occurs in these compounds, discarding the existence of intrinsic magnetoelectric multiferroicity

Magnetoelectric and structural properties of Y2CoMnO6: The role of antisite defects

We have carried out an investigation on the magnetoelectric properties of the presumed multiferroic Y2CoMnO6 with different degrees of Co/Mn atomic ordering. The magnetic ground state was studied by neutron diffraction, showing a collinear ferromagnetic (FM) ordering of Co and Mn moments with a small antiferromagnetic canting. No superstructure peaks from an E-type magnetic structure were detected in our measurements. Magnetic measurements reveal FM transitions with pinned magnetic domains. The degree of Co/Mn ordering affects the Curie temperature only a little, but has strong effects on the magnetic hysteresis loops, and the FM moment signal at high field increases with increasing such order. The loops display steps at critical fields whose number and extent depends on each specimen. The most ordered sample exhibits the greatest steps ascribed to the alignment of magnetic domains separated by antiphase boundaries. All samples are insulators exhibiting low dielectric loss and dielectric constants at low temperature. On warming, they show a step increase in the real dielectric permittivity accompanied by peaks in the dielectric loss typical of thermally activated hopping processes. At room temperature, the huge values of the dielectric constant reveal the presence of Maxwell-Wagner depletion layers. Pyroelectric measurements reveal a high polarization at low temperature for these compounds that increases with increasing the Co/Mn ordering. There is no correlation between the magnetic transition and the onset of pyroelectric current. No significant changes are observed in the pyroelectric effect measured under an external magnetic field, so magnetoelectric coupling is negligible. This paper identifies the pyroelectric current as thermally stimulated depolarization current ascribed to the reorientation of defect dipoles with activation energy of about 0.05 eV. Therefore, no ferroelectric transition occurs in these compounds, discarding the existence of intrinsic magnetoelectric multiferroicity.For financial support we thank the Spanish Ministerio de Economía y Competitividad (MINECO) (Projects No. MAT2012-38213-C02-01 and -02 and No. MAT2015-68760-C1-1 and -2-P, cofunded by the European Regional Development Fund [ERDF] from the European Union) and Diputación General de Aragón (DGA, project E-69). J.A. Rodríguez-Velamazan acknowledges CSIC for the JAEdoc contract.Peer Reviewe